The beneficial effects of increased dietary intake of long-chain omega-3 fatty acids in humans has been well documented, and includes the reduction of cardiovascular and inflammatory disease (i.e. arthritis and atherosclerosis), reduction of depression, increasing length of gestation in the third trimester, and inhibiting tumor growth. These lipids may be obtained from, for example, a number of heterotrophic marine organisms.
Besides beneficial fatty acids and lipids, many other desired substances, such as, for example, chemicals, nutritional products, proteins, antioxidants, carbohydrates, and other bioactive components, may be obtained from plant, animal, and/or microbial materials or biomass. A general scheme for obtaining these substances includes obtaining a biomass, preparing the biomass for extraction, and subjecting the biomass to extraction, i.e., separating the desired substance from the remainder of the biomass.
A number of different processes have been utilized to prepare a biomass for extraction. Generally, such processes have been ‘wet’, i.e., carried out with the addition of solvent. For example, for a fermentor-grown microbial biomass, a solid/liquid separation may be carried out to separate the cells from the fermentation broth, and a solvent added back prior to a homogenization step. Generally, a homogenization step requires addition of solvent to allow for efficient homogenization, a disadvantage in that the solvent must be removed before further processing of the biomass. The homogenization step may be carried out by a number of different processes, such as by the use of bead mills, grinding, and so on. See, for example, U.S. Pat. Nos. 4,296,099, 4,349,540, 4,429,969, and 4,455,298, all of which disclose grinding processes to prepare extracts from biological materials. These references, among others, have taught homogenization at various temperatures, such as, for example, room temperatures, elevated temperatures, freezing temperatures, and brittleness temperatures. For example, Kamarei, U.S. Pat. No. 4,776,173, teaches cryogrinding at brittleness temperatures in order to minimize particle size and avoid the use of solvent during the comminution of biomass step.
Generally, for recovery of oil from microbial biomass, extraction is begun from a biomass which has been subjected to drying and/or washing, without an accompanying cell breakage step. See, for example, Barclay, U.S. Pat. No. 5,340,594 and Bijl, U.S. Pat. No. 6,441,208. These publications generally teach a pretreatment step of a wet biomass cake including a drying step to remove water, to reduce problems such as emulsions forming upon organic solvent extraction, and to reduce the amount of solvent needed. Other publications describe crushing a dried biomass in a ball mill. However, none of these publications teach the present invention's novel methods for preparing a biomass for extraction. Surprisingly, the methods of the present invention provide many benefits that would not be expected, including an unexpected increase of yields of desired products during subsequent extraction processes.
In extraction processes, the physical form of the feed, e.g., the particle size and density, can affect the efficiency of the process. This efficiency can be determined in terms of using less solvent or energy, faster processing rate, higher percent recovery, and higher quality of the final products. Generally, it is important that the particle size be small, in order to expose as much as possible of the molecular species to the solvent. However, small particle sizes can cause difficulties in solid-liquid separation, clogging or a high pressure drops across certain types of extractors such as for example, percolation extractors. However, larger particle sizes, due to reduced contact between solvent and desired substance, tend to decrease yields.
Accordingly, although there exist in the art a number of processes to prepare a biomass for extraction, there remains a need in the art to maximize the yields and effectiveness of extraction steps, to improve the economy of these time consuming and expensive processing steps. Such preparation methods can be improved to result in subsequent extraction steps having greater yields; improve quality of the extracted products; and increase ease of extraction.